A Cellular MicroRNA, let-7i, Is a Novel Biomarker for Clinical Outcome in Patients With Dilated Cardiomyopathy

Background: Our previous studies have reported that activation of Toll-like receptor (TLR) 4 is implicated in the etiology of human dilated cardiomyopathy (DCM). A recent report has demonstrated that let-7i, a member of the let-7 family of cellular microRNAs (miRs) miR-21, miR-126, and miR-155, directly regulate TLR4 expression. The aim of this study was to determine whether let-7i, miR-21, miR-126, and miR-155 are expressed with TLR4 in human DCM, and whether let-7i levels are related to clinical outcomes. Methods and Results: Endomyocardial biopsy tissues were obtained from 103 patients with DCM and 37 subjects without left ventricular (LV) dysfunction as control subjects. Levels of let-7i, miR-126, and miR-155 were lower in the DCM group than in the controls, whereas levels of miR-21 and TLR4 (both mRNA and protein) were higher in the DCM group than in the control group. Levels of let-7i were negatively correlated with TLR4 protein levels in all subjects. After a mean follow-up period of 509 days, 6 DCM patients (5.8%) had died due to a cardiac cause and 15 (14.6%) had developed heart failure. When patients with DCM were divided into tertiles according to let-7i levels, log-rank analysis showed that the DCM subgroup with low let-7i levels was associated with poor clinical outcomes (P = .02). Conclusions: A decrease in let-7i may be related to poor clinical outcomes in patients with DCM. (J Cardiac Fail 2011;17:923-929)